RCW 9.41.220

Unlawful firearms and parts contraband.

All machine guns, short-barreled shotguns, or short-barreled rifles, or any part designed and intended solely and exclusively for use in a machine gun, short-barreled shotgun, or short-barreled rifle, or in converting a weapon into a machine gun, short-barreled shotgun, or short-barreled rifle, illegally held or illegally possessed are hereby declared to be contraband, and it shall be the duty of all peace officers, and/or any officer or member of the armed forces of the United States or the state of Washington, to seize said machine gun, short-barreled shotgun, or short-barreled rifle, or parts thereof, wherever and whenever found.